Core B is designed to provide centralized, specialized animal care for several strains of mice to include breeding colonies and purchased animals. Breeding of immuno-deficient and transgenic mice is required for our studies, as many of these strains are not commercially available, either in the quantities needed for our studies or at all. The large number of mice to be transplanted and monitored for engraftment represents the other major function of this core. In addition Core B will provide genotyping for transgenic mice bred under the auspices of this centralized core. We believe providing the expertise centrally for these service is efficient both scientifically and financially, and more important, makes is possible for all Projects to make rapid and effective use of several sophisticated mouse transplantation models.